You can buy the Kevin Kling-Chris Monroe picture book, "Big Little Brother," for $17.95 and read it to your child. Or you can buy the iPad app of "Big Little Brother" for $7.99 and hear Kling read it himself -- and also watch the characters move and hear the toys talk.

Book apps for tablets and smartphones and enhanced e-books for e-readers are going far beyond the transfer of book text to Kindle screen. By bringing audio, video, animation and games to what was once the simple printed page, apps are beginning to fundamentally change our understanding of what makes a book a book.

So far, the trend has been cautious, but publishers predict enhancements will be common within two years. "It's clearly a market waiting to be fed," said Corinne Helman, vice president of digital publishing and business development for Harper Collins children's books. "This is still very, very early days."

"I think this is going to be a huge deal," said Dan Leary, design and production manager for the Minnesota Historical Society Press. "It's really changing what a book is."

Book apps can be as modest as "Big Little Brother," with just a little animation and audio. Or they can be as elaborate as "Fancy Nancy Dress Up," which allows children to design outfits, dress Fancy Nancy and drop her into the story.

Enhanced e-books include all kinds of supplemental material: travel books are embedded with film clips, language books with audio, cookbooks with step-by-step videos.

There are even book apps that have never been printed books, such as David Sedaris' "David's Diary," six animated videos inspired by his diary entries.

Image-heavy books, such as picture books and photo books, lend themselves well to apps. "The iPad does images better than you can print them," Leary said. "The quality is like a transparency in a lightbox."

Made for images

Minnesota photographer Jim Brandenburg turned his award-winning 1998 book, "Chased by the Light," into an app. It contains the original images of northern Minnesota, additional photos from the revised softcover edition, "After the Storm," and 17 video clips from the documentary about the book.

"Each of the video clips are positioned right on that image," said Heidi Brandenburg, the photographer's daughter and manager. "So as you look at it, Jim is talking about why he chose that subject and what he was thinking."

You can also toggle from an original image to a photo of the same place, taken since the BWCA blowdown. "This is our very first app, but it won't be our last," Brandenburg said. "For photography, it's just unbelievable. It gives a whole new life to the images."

Move over, mom and dad

Apps of children's books are particularly attractive to busy parents, Helman said. "How often do you whip out a phone and say, 'I'll buy myself 20 minutes of silence?' I think parents feel good about book apps because it's still a book and the child is still learning."

If parents are too busy to read to the child -- or have already read the book aloud 50 times -- the app can take over. "It means, in some respect, that the kid is now spending more time with books because it doesn't require the parent to be there," Helman said.

This gives Phyllis Root pause. "If it gets children interested in books, it's good," said Root, the Minneapolis author of more than 40 books for children and an instructor in Hamline University's MFA program in writing for children. "But the most important thing about a picture book is that you sit down and read it with a kid."

A parent can point to a picture and say, "What sound does a frog make?" Root said. "And the child might make the sound. But if every time you come to that page you can push the frog and it makes a noise, you've handed over some of the interactiveness of the picture book to this prepackaged shape."

Lori Helman, associate professor of literacy education at the University of Minnesota and co-director of the Minnesota Center for Reading Research (and no relation to Harper Collins' Corinne Helman), said human relations are crucial to child development.

"We need a lot of opportunities for face-to-face interaction so children can learn what it means to be human," she said. "A developing person, whether they're 2 or 7, needs to be able to ask questions and check out their understanding. And no app can be responsive to all the questions and thoughts and wonderings that a young person needs. You need people."

That said, Helman added, apps and e-books can give kids more access to books and put libraries at their fingertips.

"If we're using these things as little babysitters, I think kids will get tired of them," she said. "But if we use them to enhance our interaction, imagine the great conversation that could spark."

Slow growing for now

While technology is fueling this trend, it is also slowing it down.

Apps must be written one way for Apple products, another way for Droids. App stores don't have a separate category for book apps, making them hard to find. And devices are changing so fast that no one dares invest too heavily in any one direction.

"It's been a sort of three steps forward, three steps back," said Terry Adams, who heads e-book and digital publishing for the Hachette Book Group, which includes Little, Brown. "It is the wild, wild West in this marketplace."

All that additional content requires negotiation and money. "If our agreement with an author is a basic book agreement, there are rights related to images and sound and whatever that are not part of that," Adams said. "So that material has to be provided and paid for. It's very expensive."

Still, Harper Collins' Helman said she thinks these are temporary obstacles. "The publishing industry is trying to get together to figure this out," she said. "There's no doubt in my mind that the standard will be achieved. This is just momentary noise."

The biggest concern, Leary says, is permanence.

"The best long-term storage of anything is the book," he said. "It's still the most future-proof thing in this office. The book version of the Kling-Monroe project will still be functional in 50 years. The iPad version of the book -- I will be surprised if anyone has a device that will still be functional in 10 years.

"These things will have a two-year life span, and then you develop for the next piece of technology."